The present invention relates to an apparatus separating sludge from a liquid and may be advantageously used in conjunction with a spray booth wherein water is used to remove oversprayed particles from the air.
The spraying of coatings such as paints, enamels, lacquers, etc. is commonly conducted in booths in which a flow of air transports oversprayed particles and volatile organic solvents away from the worker. An efficient method of removing oversprayed particles from the air within such a booth is to provide water washes in the path of the coating spray and/or air flow, the water washes trapping the airborne particles. A spray booth of this type is disclosed in U.S. Pat. No. 4,484,513, issued on Nov. 27, 1984, which is herein incorporated by reference. In such spray booths, the trapped paint particles travel with the water to a holding tank from which the water is recirculated to the water washes. Most holding tanks have chemicals added to the water therein for agglomerating the paint spray particles, and many of the agglomerated particles form a floating piece of sludge.
While water wash spray booths have effectively cleaned the air that is exhausted from the spray booth, the problem remains of how to dispose of both the agglomerated spray particles cleaned from the air and the water used to clean the air. For example, when solvent-based coatings are used in the spray booth, significant amounts of hydrocarbons may be released into the air, not only during initial spraying, but also as they evaporate from the agglomerated oversprayed particles floating in the water in the holding tank. Further, discharge of the water utilized in the spraying booth presents a substantial waste disposal problem. Due to the solvents, paint particles and the paint agglomerating chemicals contained therein, the water may not be directly discharged into sewage systems. Because of problems associated with disposal of the water, it is desirable to use the water for as long as possible before replacing it. However, concommitant with the use of the water is the need to prevent the formation of septic conditions therein. Although certain chemicals may be used to prevent septic conditions in the water, such chemicals add further to the pollution problem entailed in the eventual discharge of the water.
Because the sludge contains, in part, recoverable pigments, it may, in some instances, if collected, be recycled by chemical companies. Often the maintenance of the spray booth had involved the periodic skimming of sludge from the tank and the dispatching of a crew to drain and manually scrape sludge from the bottom of the holding tank.
A sludge separation device that addresses the concerns discussed above is disclosed in U.S. Pat. No. 4,432,870, issued Feb. 21, 1984, and herein incorporated by reference. The device of the patent employs a separate sludge removal tank from which floating sludge is transferred to a collection bin by means of a reciprocating skimmer. The present invention constitutes an improvement over the above-referenced sludge separation device in that the water levels of the holding tank and the separation tank are no longer required to be substantially the same in order for liquid and sludge to be transferred therebetween, thereby making the retrofitting of existing spray booths with the inventive separation device not dependent on the elevation of the holding tank of the spray booth. Collaterally, the inventive separation device removes the requirement that the water levels in the respective tanks be precisely controlled in order for sludge and liquid to be transported from the holding tank to the separation tank and for clarified liquid to be returned from the separation tank to the holding tank. Additionally, the drive system for reciprocating the skimmer that forms a part of the separation device is improved so as to be subjected to fewer stresses during the course of operation and less likely to come in contact with contaminating and corroding sludge and water during the course of operation.